This application claims the priority benefit of Taiwan application Ser. no. 91101024, filed Jan. 23, 2002.
1. Field of Invention
The present invention relates to a metal post manufacturing method. More particularly, the present invention relates to a metal post manufacturing method that involves the conduction of a transient electric arc welding using a conductive electrode. The metal posts serve as via plugs on a ceramic circuit board, a soft or hard plastic circuit board, a glass substrate or a silicon wafer.
2. Description of Related Art
Due to rapid progress in the electronic industry, electronic products continue to shrink in size and increase is functional capacity. In chip packaging area, ball grid array (BGA) and chip scale (CS) packages are developed through market""s demand for miniaturization and highly integrated packages. In the manufacturing of printed circuit boards, a multi-layered structure is introduced to reduce area occupation of electronic circuits. To connect various circuit layers within the substrate of a ball grid array package or a chip scale package, a multi-layered printed circuit board or a wafer, conductive via plugs are often formed. Hence, dimensions of minor circuits and plugs within the substrate layer will largely affect the packing density of a package and the level of integration of a printed circuit board and a wafer.
FIGS. 1 through 9 are schematic cross-sectional views showing the progression of steps for forming a conventional build-up substrate board. As shown in FIG. 1, an insulating core layer 100 having a conductive layer 102 on each side of the core layer 100 is provided. In general, the conductive layers 102 are copper layers.
As shown in FIG. 2, a plurality of through holes 104 are formed in the insulating core layer 100 by laser drilling or mechanical drilling. A conductive layer 106 is formed on the sidewalls of the through holes 104 as well as the two surfaces of the insulating core layer 102. The conductive layer 106 is also a copper layer. The conductive layer 106 is formed, for example, by forming a seeding layer before conducting an electroplating operation.
As shown in FIGS. 3 and 4, a hole-filling operation is carried out. An insulating material 108 is deposited into the through holes 104. The purpose of filling the through hole 104 is to prevent the intrusion of any moisture. Any moisture that gets into the through hole 104 may expand in the presence of heat to form popcorn-like bubbles. Thereafter, any insulating material 108 above the insulating core layer 100 is ground down to a suitable roughness level.
As show in FIG. 5, a conductive layer 110 is formed over the second surface of the insulating core layer 100 globally. The conductive layer 110 covers the exposed insulating material 108 above the insulating core layer 100. The conductive layer 110 is formed, for example, by forming a seeding layer before conducting an electroplating operation.
As shown in FIG. 6, the conductive layer 110 on each side of the core layer 100 is patterned by coating a photoresist layer, conducting photo-exposure, developing the photoresist, etching the conductive layer 110 and removing the photoresist layer.
As shown in FIG. 7, a dielectric layer 112 is formed over each side of the insulating core layer 100. The dielectric layer 112 has a plurality of openings 114. Each opening 114 exposes a portion of the conductive layer 110.
As shown in FIG. 8, a conductive layer 116 is formed over the dielectric layers 112, the sidewalls of the openings 114, and the exposed conductive layer 110. The conductive layer 116 is formed, for example, by forming a seeding layer before conducting an electroplating operation.
As shown in FIG. 9, conductive material is deposited into the openings 114 to form a plurality of via plugs 118. The conductive layer 116 is patterned by coating a photoresist layer, conducting photo-exposure, developing the photoresist, etching the conductive layer 116 and removing the photoresist layer.
In the conventional build-up substrate manufacturing method, the conductive layers 110 are electrically connected through a plug formed by a plating through-hole (PTH) process. The conductive layer 110 and the conductive layer 116 are electrically connected through a via plug 118. In other words, to produce the build-up substrate, holes must be drilled to form the through holes 104, electroplating must be conducted to form the conductive layers (106, 110 and 116) and insulating material 108 must be deposited to fill the through holes. Hence, the conventional fabrication method is both time consuming and complicated.
Moreover, as the level of integration increases and the size of through holes 104 reduces to a diameter of 100 xcexcm or less, the conventional method no longer can provide a suitable means of fabrication.
Accordingly, one object of the present invention is to provide a metal post manufacturing method capable of producing via plugs having a dimension ranging from 1 to 200 xcexcm. The metal post manufacturing method according to this invention is able to replace the conventional plating through-hole (PTH) process.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a metal post manufacturing method. A fixture having an array of wire guide heads thereon is provided. Each wire guide head contains a conductive wire. A substrate receiving the metal posts is put under the wire guide heads of the fixture. The wire guide heads utilize the production of a transient electric arc to generate the energy necessary for transforming one end of the conductive wire into a dangling block of material having a teardrop shape underneath the guide head. Simultaneously, the entire fixture moves and pulls the array of wire guide heads down to form a plurality of metal posts over the substrate.
In this invention, the conductive wire is made from a material such as aluminum, gold, silver, copper, platinum, zinc or lead-tin alloy. Alternatively, the conductive wire may contain a core material enclosed by one or more conductive material layers such as a copper layer enclosing a lead-tin core, a lead-tin layer enclosing a copper core or a tin or a silver layer enclosing an alloy steel core. In addition, the conductive wire may have a diameter ranging between 1 to 200 xcexcm.
In this invention, the wire guide heads move towards the substrate so that the teardrop shaped block of conductive material may attach to the substrate. Thereafter, the wire guide heads are pulled in the opposite direction away from the substrate so that height level of the metal post can be properly set. Height level of the metal posts may be modified according to the specification. To form a metal post having a height over the dielectric layer about 1 to 10 xcexcm, a teardrop shaped block of conductive material is repeatedly formed over the one already attached. In addition, dimension of the metal posts can be controlled by choosing conductive wires with the optimum diameter, from smaller than 50 xcexcm, between 50 to 100 xcexcm, between 100 to 200 xcexcm to 200 xcexcm and beyond.
The metal post manufacturing method according to this invention may also be applied to the fabrication of a printed circuit board, the substrate (carrier) of a package or a wafer.
This invention also provides a method of forming a build-up substrate board. A carrier having a first conductive layer thereon is provided. The aforementioned metal post manufacturing method is applied to form a plurality of first metal posts over the first conductive layer. A first dielectric layer is formed over the first conductive layer. The first dielectric layer encloses the first metal posts but the upper ends of the first metal posts are exposed. A second conductive layer is formed over the first dielectric layer. Removing the carrier, the first conductive layer and the second conductive layer are concurrently patterned. Finally, a build-up process is carried out to form material layers over the first and the second conductive layer.
In this invention, the first dielectric layer is formed, for example, by placing a sheet-shaped dielectric layer over the carrier. The first metal posts pierce through the sheet-shaped dielectric layer. The first dielectric layer may also be formed by spin coating operation or curtain coating, especially for a very fine metal post processing.
After forming the first dielectric layer, a curing operation of the first dielectric layer may be carried out. Thereafter, the upper ends of the metal posts are pressed in a coining operation or laminated with the copper foil.
In the build-up process, second metal posts may form over the substrate by conducting the same metal post manufacturing method. A dielectric layer and a conductive layer are sequentially formed. The conductive layer is patterned. The number of layers formed by the build-up process depends on actual requirements.
To pattern the conductive layer, a seed layer is formed over the dielectric layer before forming the conductive layer. Thereafter, a patterned photoresist layer is formed over the conductive layer. The conductive layer and the seed layer outside the photoresist layer are removed together. Finally, the photoresist layer is also removed.
In an alternative method of patterning the conductive layer, a seed layer is formed over the dielectric layer before forming a patterned photoresist layer over the seed layer so that a portion of the seed layer is exposed. Thereafter, a conductive layer is formed over the exposed seed layer. The photoresist layer is removed. Finally, the seed layer and a fraction of the thickness of the conductive layer are removed through a flash etching operation. In a flash etching operation, fine circuit lines are produced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.